Middle-latitude ionospheric total electron content: Summer 1965

The total electron content of the ionosphere was measured continuously from a northern mid-latitude station during the summer of 1965 by monitoring the polarization twist of VHF radio signals from the Early Bird synchronous satellite. The ambiguity in the total amount of polarization twist of the Early Bird signal was resolved by measuring the total polarization twist of a lunar reflected radio wave at a time when the moon coincided in direction with Early Bird. Large day-to-day differences in electron content were seen. The late afternoon maximum value of electron content was not well related to magnetic activity. Many small, irregular changes in electron content were observed. Diurnal values of electron content were much lower than those observed during 1961. Observations of polarization twist of VHF radio waves from synchronous satellites provide a simple, accurate means of measuring diurnal, seasonal, and anomalous changes in ionospheric total electron content.